The present invention refers to a clamping apparatus, comprising a clamping chuck and a work piece carrier adapted to be releasably connected to the clamping chuck, having a flat bottom surface and comprising a clamping pin protruding from the flat bottom surface. The clamping chuck comprises a central opening with a conical inserting portion for receiving the clamping pin of the work piece carrier. The clamping pin comprises at least one surface portion corresponding in shape to the shape of the conical inserting portion of the central opening for aligning the position of the clamping pin in X- and/or in Y-direction. Moreover, the clamping chuck is provided with a clamping mechanism for clampingly fixing the clamping pin of the work piece carrier in the central opening, and at least one surface portion serving as a Z-direction stop member.
Such a clamping apparatus is preferably used for clamping work piece carriers equipped with one or several work pieces to be machined in the machining area of a machine tool in a well defined and predetermined position. Usually, the clamping chuck of the apparatus is fixed in the machining area of the machine tool, while the work piece carrier, provided with a clamping pin, is releasably attached to the clamping chuck.
In order to be in a position to clamp work pieces with different dimensions, so-called palletizing systems are known which comprise a plurality of clamping chucks, usually two, four, six or eight of them. By means of these plurality of clamping chucks, a work piece carrier equipped with, depending on its size, two, four, six or eight clamping pins can be clamped. In certain cases, it may happen that the work piece carrier is equipped with an odd number of clamping pins. Since an individual clamping chuck usually comprises neither means to avoid a rotation of the clamping pin nor means for determining the angular position of the clamping pin around the Z-axis, it can be advantageous to provide one or several clamping chucks with positioning means, determining besides the X- and Y-positions also the angular position around the Z-axis, with the result that, if appropriate, also work piece carriers having but one clamping pin can be clamped to the clamping chuck in an exactly defined linear and angular position. It is understood that in such a case also the work piece carrier has to be provided with positioning means cooperating with the above mentioned positioning means of the clamping chuck.
A difficulty observed particularly in connection with large and heavy work piece carriers may be seen in the fact that a required coarse aligning of the clamping pins of the work piece carrier with the corresponding openings in the clamping chucks is pretty difficult because there is only a small clearance between the front portion of the clamping pin and the opening in the clamping chuck adapted to receive the clamping pin. Moreover, there is a danger that both the clamping pin and the opening in the clamping chuck may be damaged.
Besides clamping apparatuses in which the clamping pin is provided with a cylindrical portion for its positioning within the opening of the clamping chuck, other clamping apparatuses are known in the art in which the clamping chuck is provided with a conical centering surface area for a clearance-free aligning of the clamping pin. For example the document EP 1,044,760 discloses a clamping apparatus of this kind. In this clamping apparatus, the clamping pin is aligned by means of a conical centering surface provided at the top of the opening of the clamping chuck. The housing wall of the clamping chuck is axially resilient in the region of this conical centering surface; for this purpose, a radial cutout is provided behind the conical centering surface. Thereby, an elastically resilient area is created which enables the clamping pin to be axially moved and to be pulled in further in Z-direction after having been centered. Elastically resilient surface areas of this kind have shown to be efficient particularly in small clamping apparatuses. However, in the case of clamping apparatus adapted to receive large and heavy work piece carriers, the clamping chuck is lastingly weakened by the provision of such a cutout. Moreover, it is not possible to provide a Z-reference or a Z-direction stop member in the area around the above mentioned cutout since the clamping apparatus is too resilient in Z-direction in that area. Finally, there is a danger that the elastically resilient area is damaged upon inserting the clamping pin into the clamping chuck because the elastically resilient area cannot bear high loads neither in axial nor in radial directions.
The document DE 41 10 857 discloses an apparatus for coupling a tool holder to a working spindle of a machine tool. The working spindle is provided with an opening for receiving a shaft portion of the tool holder. The opening has an upper and a lower conical portion with an annular recess having a supporting surface located between the two conical portions. The shaft portion of the tool holder is equipped with two cone rings supported by elastic abutments. Between the two cone rings, a locking mechanism is located, comprising two radially movable locking pieces. On the top, these locking pieces are provided with wedge shaped surface areas which rest in the locked state on the supporting surface of the annular recess. By providing the elastic abutments, the cone rings are axially movable relative to the shaft portion of the tool holder and enable the shaft portion to be pulled in into the opening after the cone rings having been rested on the conical portions of the opening. The cone rings themselves are provided with slots. The shaft portion is provided with a flange portion constituting at its lower end a flat annular surface serving as a Z-direction stop member, resting on the front face of the working spindle upon clamping the shaft portion. In the opening of the working spindle, both conventional clamping pins (FIG. 5) and sectional clamping pins (FIGS. 1 and 3) can be clamped. Thus, the basic idea of the invention may be seen in the fact that work piece carriers with differently designed clamping pins can be clamped by the working spindle of the machine tool. It is understood that such a clamping apparatus is not at all suitable for attaching a work piece holder to the working spindle of a machine tool in a highly precise and repeatable manner.
U.S. Pat. No. 5,722,806 discloses a coupling system that includes a male coupling having a cylindrical distal end including a recess that includes follower surfaces, a female coupling having a cylindrical interior for receiving the distal end of the male coupling, and a pair of opposing jaw members movably mounted within the interior and including external cam surfaces for engaging the follower surfaces of the male coupling when the jaw members are radially moved apart, and a drive train for radially and forcefully moving the jaw members apart. The drive train includes a wedging ball that freely floats in recesses between the opposing jaw members, and a drive rod for axially moving the wedging ball into and out of engagement with wedge surfaces located in the interior of the jaw members. The drive rod includes a distal end having a bore for slidably receiving the wedging ball. The free-floating of the wedging ball within the drive rod bore and between the internal surfaces of the jaw members allows it to apply uniform wedging forces to the jaw members when spreading them apart into a coupling position.
U.S. Pat. No. 5,918,870 discloses a device for detachable fastening of work pieces to be machined on a processing machine having a pallet on which the work pieces are detachably fastened, and which can be connected detachably via this pallet to the processing machine, wherein the locking between the pallet and one or more quick-clamp cylinders is effected through at least one pull-in bolt which are fastened on the pallet and which engage in clamping manner in corresponding receptacles on the quick-clamp cylinder, and wherein the clamping connection is maintained through tension springs, and for unlocking a hydraulic piston can be actuated which overcomes the clamping force of the tension springs, wherein in the quick-clamp cylinder the space between the central pull-in bolt and the tension springs arranged to the side of the latter is sealed.
U.S. Pat. No. 5,415,384 discloses an apparatus for clamping a work piece comprising a base and a work piece carrier adapted to be put onto and fixed to the base. The base and the carrier comprise aligning means to align the position of the carrier relative to the base along three perpendicular coordinate axes as well as the angular position. The aligning means comprises first aligning element pairs in the form of cooperating reference surfaces at the carrier and the base, which define the position of the carrier in the Z-axis. The aligning means further comprises second and third aligning element pairs in the form of cooperating linear aligning element pairs, which define the position of the carrier in the X and Y-axes, respectively. The cooperating pairs each comprise a wedge-shaped centering member and a counterpart member with a matching centering slit. Clamping means is provided for clamping the carrier to the base in a well defined position which is defined by the aligning means. The clamping means comprises a plurality of clamping members, each including a pin member fixed to the carrier and a chuck member located in the base. The carrier comprises a flat surface which faces the base if the carrier is clamped to the base. The flat surface forms one of the reference surfaces. Each one member of the second and third pairs is directly connected to the flat surface. Each pin member is also directly connected to the flat surface.
It is an object of the invention to provide a clamping apparatus with a clamping chuck and a work piece carrier releasably connected thereto whose clamping chuck is particularly suitable for palletizing systems, whereby the individual clamping chuck shall be very robust and rigid.
It is a further object of the invention to provide a clamping apparatus with a clamping chuck and a work piece carrier releasably connected thereto in which the clamping pin is aligned in X- and/or Y-direction without any clearance.
It is a still further object of the invention to provide a clamping apparatus with a clamping chuck and a work piece carrier releasably connected thereto in which a movement of the clamping pin and, thereby, the work piece carrier in Z-direction is possible after the clamping pin has been aligned in X- and/or Y-direction, without the need to provide separate elastically resilient means.
In order to meet these and other objects, the invention provides a a clamping apparatus, comprising a clamping chuck, and a work piece carrier adapted to be releasably connected to the clamping chuck, having a flat bottom surface and comprising a clamping pin protruding from the flat bottom surface. The clamping chuck comprises a central opening with a conical inserting portion for receiving the clamping pin of the work piece carrier. The clamping pin comprises at least one surface portion corresponding in shape to the shape of the conical inserting portion of the central opening for aligning the position of the clamping pin in X- and/or in Y-direction. Moreover, the clamping chuck is provided with a clamping mechanism for clampingly fixing the clamping pin of the work piece carrier in the central opening, and at least one surface portion serving as a Z-direction stop member.
The clamping pin is dimensioned such that, prior to activating the clamping mechanism, a gap exists between the flat bottom surface of the work piece carrier and the surface portion of the clamping chuck serving as a Z-direction stop member, after the clamping pin of the work piece carrier having been inserted into the central opening of the clamping chuck with the surface portion of the clamping pin having engaged the conical inserting portion of the central opening and, thereby, having aligned the clamping pin with reference to the clamping chuck in X- and/or Y-directions. Thereby, the clamping pin and/or the region around the central opening of the clamping chuck is/are adapted to be elastically deformed upon activation of the clamping mechanism to further pull in the clamping pin into the central opening and simultaneously the work piece carrier towards the surface portion of the clamping chuck serving as a Z-direction stop member until the flat bottom surface of the work piece carrier rests on the surface portion of the clamping chuck serving as a Z-direction stop member.
Thus, the basic idea of the invention may be seen in the fact that the clamping pin is designed in such a way that it can align itself without clearance in X- and/or Y-direction upon insertion into the opening of the clamping chuck without the work piece carrier resting on the clamping chuck. In other words, during that aligning of the clamping pin, a small gap remains between the bottom surface of the work piece carrier and the top surface of the clamping chuck. This gap is removed when the clamping pin is further pulled in into the opening of the clamping chuck by means of the clamping mechanism, whereby the material elasticity of the clamping pin and/or of the region of the clamping chuck around the central opening is used for that purpose. Thereby, the work piece carrier is moved in Z-direction towards the clamping chuck until its flat bottom surface rests on the Z-direction stop member constituted by the corresponding surface areas on top of the clamping chuck. In this way, the provision of means that are elastically resilient in Z-direction can be totally avoided.